1. Field of the Invention
The present invention relates to a dielectric filter and, a transmitter-receiver antenna sharing device (duplexer) and a microwave band and/or milliwave band communication device using same.
2. Description of the Related Art
Recently, communication systems with large capacity and high speed transmission are being required corresponding to a rapid increase in the demand for mobile communications, including multimedia. Accompanying this expansion of the required information-carrying capacity, the frequency band used is being raised from the microwave band to the milliwave (millimeter-wave) band. Even in such milliwave band, the TE01 delta mode dielectric resonator which has been conventionally used in the microwave band can be similarly used, but a resonance frequency thereof is determined by a dimension of a cylindrical shaped dielectric, and for example, at 60 GHz, since it will be very small as a height thereof being 0.37 mm, and a diameter thereof being 1.6 mm, a severe manufacturing precision is required. Further in case of constituting a filter using the TE01 delta mode dielectric resonator, it is required to place a plurality of the TE01 delta mode dielectric resonators in a predetermined space with a high positioning precision, and a further problem is that the structures for trimming the amount of a resonance frequency for each resonator and for trimming coupling between the dielectric resonators are complex.
Accordingly, the applicant of the present application has proposed the dielectric resonator and the band-pass filter by which these problems were solved, in the Japanese Patent Application No. 7-62625 (EP 0 734 088 A1.
Now, in this resonator and the corresponding filter, electrode non-formation parts on the dielectric plate are configured to form dielectric resonators. Electrodes are formed on both main surfaces of such dielectric plate and openings, i.e., electrode non-formation parts, are formed in the respective electrodes at positions opposite to each other. Only one resonance mode of the dielectric resonators is used, by drawing a coupling member to be coupled to the dielectric resonators near the dielectric resonators, as well as, by placing a coupling member used for an input and a coupling member used for an output on a straight line, or in parallel, with respect to the dielectric resonators.
However, in a blocking region attenuation characteristic, when a large attenuation quantity is necessary for a certain frequency, the requirement may not be satisfied by the conventional structured dielectric filter as described above. In particular, in interstage filter, an oscillation frequency of a local oscillator and an attenuation quantity at an image frequency present problems. Further, in an antenna common use device, the attenuation at receiving frequencies in a transmitting side filter, and the attenuation at transmitting frequencies in a receiving side filter present problems, respectively.